I dont know how people use knuckle booms in the sign industry. so bulky. If you are asking my opinion I would keep the 40' truck you have unless it gives you problems. I couldn't imagine NOT having a smaller truck that can get in anywhere and close to buildings for service work and installs. keep the 40' for backup, im sure it doesn't owe you anything anymore. if it is still reliable then hang onto it. Keep the wilke for bigger lifts and get a sx57 on a single axle with front and rear outriggers and make that into your rolling shop. Good boxes with roll out drawers, welder with cables on reels, tanks with lines on a reel, water tank, ladders on the boom. trailer hitch ect.